Line interface units (LIU) are used for interfacing between a communication medium (often referred to as a line) and a communication device. For example, in wired Ethernet a LIU may be situated between a system ASIC (Application Specific Integrated Circuit) which is a communications device and a set of magnetics which are attached directly to a wired line. FIG. 3 illustrates, generally at 300, a board 302 having a system ASIC 304 connected via 305 to a LIU (often referred to as a PHY (Physical layer device)) 306 which in this example is connected via 307 to magnetics 308 which interface to line 309. The magnetics provide isolation.
A LIU (such as illustrated by FIG. 3) uses powered, discrete mixed signal semiconductor ICs (Integrated Circuits) mounted on printed circuit boards and connected to passive magnetics modules and line transformers.
If the semiconductor technology changes, then a different transformer ratio is needed. If a board containing this line transformer is already installed in the field, then it cannot be easily replaced. This presents a problem.
There may be unnecessary cost and complexity of a total solution which includes separate transformers, protection components, bypass capacitors and termination resistors. This presents a problem.
High density is possible in the ICs (e.g. 32 channels), however, the same level of density is limited in the line transformers, and the cost of higher density ICs may lead to an overall increase in per-port cost. This presents a problem.
Compliance of the complete line interface solution to specifications is not assured because IC, protection, and transformers are delivered to the customer by at least two different suppliers. This presents a problem.
The line interface IC is connected to power, digital logic of system level chip, and analog signal at the transformer. One side of the transformer is connected to the IC analog signal, the other side is connected to a twisted pair or cable which is in turn susceptible to voltage spikes and other interference. If power is lost to the IC, then basic operation of the interface, including fault reporting, is no longer possible. If the transformer is located on a different circuit board from the IC and the two parts are connected using a connector, a break in the connection between them will result in a failure that cannot easily be detected and traced. This presents problems.
A Y-cable arrangement (such as illustrated by FIG. 4) uses a bulky series of connectors and cards to achieve redundancy.
For example, in FIG. 4, generally at 400 is shown one such approach. At 401 is a twisted pair, at 402 a connector, at 403 the wires leading to connectors 404 and 406 going respectively to 410 Primary Line Card and 412 Backup Line Card. Isolation switches as ganged by 411 are shown. Not shown is one or more ASICs to the left of each line card.
FIG. 5 illustrates a current approach to redundancy, generally at 500, which shows separate processors. At 502 is processor #1, and at 504 is processor #2.